JP2013165098A - Photoelectric conversion device, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of photoelectric conversion by suppressing light absorption phenomenon on a back electrode including a light reflective metal layer.SOLUTION: A photoelectric conversion comprises: a substrate 11a; and a first conductive layer 11b, a photoelectric conversion layer 10, a second conductive layer 15, a low refractive index layer 16b and a back electrode 16 positioned in this order from a light-receiving surface side on the substrate 11a. The low refractive index layer 16b has a lower refractive index than that of the second conductive layer 15, and translucency. The back electrode 16 contacts with and is electrically connected to a part of the second conductive layer 15.

Description

  The present invention relates to a photoelectric conversion device and a manufacturing method thereof.

  As a prior document disclosing the configuration of the photoelectric conversion device, there is JP 2000-252500 A (Patent Document 1). The silicon-based thin film photoelectric conversion device described in Patent Document 1 includes a transparent electrode, a silicon-based thin film photoelectric conversion unit, and a back electrode including a light reflective metal electrode, which are sequentially formed on a substrate. Yes.

  In this silicon-based thin film photoelectric conversion device, the transparent electrode has a two-layer structure in which the first and second transparent conductive films are laminated from the substrate side, and the first transparent conductive film has an average height difference of surface irregularities of 100 to 1000 nm. In addition, the second transparent conductive film has an average film thickness of 50 to 500 nm, and the average height difference of the surface irregularities is smaller than that of the first transparent conductive film.

  With this configuration, even if the surface unevenness of the first transparent conductive film is severe, spike-like protrusions can be eliminated by smoothing the surface unevenness of the second transparent conductive film, and a short circuit between junctions in the photoelectric conversion unit can be achieved. It is possible to reduce the variation in performance of the photoelectric conversion device.

JP 2000-252500 A

NEDO achievement report (management number: 20100000000638) JOURNAL OF APPLIED PHYSICS Vol.95, No.3,1 February 2004 pp.1427-1429

  As described in FIGS. 1 and 2 of Patent Document 1, even if the surface unevenness of the second transparent conductive film is smoothed, the light reflective metal electrode is caused by the unevenness of the first and second transparent conductive films. Have irregularities.

  In the light reflective metal having irregularities, a light absorption phenomenon called surface plasmon absorption occurs depending on the material of the light reflective metal and the medium with which the light reflective metal is in contact.

  When light is incident on the light-reflecting metal surface having irregularities that cause surface plasmon absorption, the light is absorbed by the surface plasmon absorption, and the amount of light reflected on the light-reflecting metal surface is reduced. In this case, light reflected on the surface of the light-reflecting metal and re-entering the photoelectric conversion layer is reduced, which has been a factor in reducing the photoelectric conversion efficiency of the photoelectric conversion device.

  The present invention has been made in view of the above-described problems, and provides a photoelectric conversion device and a method for manufacturing the same, in which a light absorption phenomenon in a back electrode containing a light-reflecting metal is suppressed to improve photoelectric conversion efficiency. The purpose is to provide.

  The photoelectric conversion device according to the present invention includes a substrate and a first conductive layer, a photoelectric conversion layer, a second conductive layer, a low refractive index layer, and a back electrode, which are sequentially positioned on the substrate from the light receiving surface side. The low refractive index layer has a lower refractive index than the second conductive layer and has translucency. The back electrode is in contact with and electrically connected to a part of the second conductive layer.

  In one embodiment of the present invention, the substrate has translucency. The first conductive layer is located on the substrate, the photoelectric conversion layer is located on the first conductive layer, the second conductive layer is located on the photoelectric conversion layer, and the low refractive index layer is located on the second conductive layer. The back electrode is located on the low refractive index layer.

  In one embodiment of the present invention, the back electrode is located on the substrate, the low refractive index layer is located on the back electrode, the second conductive layer is located on the low refractive index layer, and the photoelectric conversion layer is the second conductive layer. The first conductive layer is located on the photoelectric conversion layer.

In one embodiment of the present invention, the low refractive index layer is composed of SiO ₂ .
Preferably, in a plan view, the contact area between the second conductive layer and the back electrode is 5.5% to 55% of the total area of the back electrode.

  Preferably, the shape of the contact portion between the second conductive layer and the back electrode is a grid shape in plan view.

  In the method for manufacturing a photoelectric conversion device according to the present invention, each layer is formed on a substrate so that the first conductive layer, the photoelectric conversion layer, the second conductive layer, the low refractive index layer, and the back electrode are positioned in order from the light receiving surface side. The process of carrying out is provided. In the step of forming the low refractive index layer, the low refractive index layer is formed of a material having a refractive index lower than that of the second conductive layer and having a light transmitting property. In the step of forming the back electrode, the back electrode is formed so as to be in contact with and electrically connected to a part of the second conductive layer.

  In one embodiment of the present invention, after the step of forming the first conductive layer, the photoelectric conversion layer is formed, and after the step of forming the photoelectric conversion layer, the second conductive layer is formed and the second conductive layer is formed. After the step of forming, the low refractive index layer is formed, and after the step of forming the low refractive index layer, the back electrode is formed.

  In one embodiment of the present invention, after the step of forming the back electrode, the low refractive index layer is formed, and after the step of forming the low refractive index layer, the second conductive layer is formed, and the second conductive layer is formed. After the step of forming, the photoelectric conversion layer is formed, and after the step of forming the photoelectric conversion layer, the first conductive layer is formed.

  According to the present invention, it is possible to improve the photoelectric conversion efficiency by suppressing the light absorption phenomenon in the back electrode containing the light reflective metal.

It is sectional drawing which shows the structure of the photoelectric conversion apparatus which concerns on Embodiment 1 of this invention. It is the top view which looked at the shape of the contact part of the 2nd conductive layer and back electrode concerning the embodiment from the arrow II direction of FIG. It is sectional drawing which shows the structure of the photoelectric conversion apparatus which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the structure of the photoelectric conversion apparatus which concerns on Embodiment 3 of this invention.

  In the present specification, “amorphous” is synonymous with “amorphous” generally used in the art. In addition, as generally used in the field, “microcrystal” includes not only a state consisting essentially of a crystalline phase but also a state where a crystalline phase and an amorphous phase are mixed.

For example, in the Raman scattering spectrum, it is considered that “microcrystalline silicon” is one in which even a sharp peak near 520 cm ⁻¹ attributed to a silicon-silicon bond in crystalline silicon is detected. “Microcrystalline silicon” is also used in the same sense in the book.

  Note that in this specification, “microcrystalline silicon germanium” refers to silicon germanium in the above-described microcrystalline state. That is, microcrystalline silicon germanium includes not only a state substantially consisting of a crystalline phase but also an amorphous silicon germanium phase and a crystalline silicon germanium phase.

  In microcrystalline silicon germanium, as described in the NEDO achievement report (management number: 20100000000638) (Non-Patent Document 1), the unit cell size of the crystal is proportional to the increase in germanium concentration. It is known to vary in the range from the unit cell size to the unit cell size of crystalline germanium.

  This means that the proportion of unit cell silicon-germanium bonds present in the microcrystalline silicon germanium layer increases with increasing germanium concentration. Therefore, the presence of the crystalline silicon germanium phase can be known by measuring the size of the unit cell using, for example, X-ray diffraction. In addition, in the analysis of the Raman scattering spectrum described later, the microcrystalline silicon is also observed when the peak attributed to crystalline silicon germanium is observed or the peak position attributed to silicon-silicon of crystalline silicon is changed. The presence of the germanium phase can be known.

Therefore, the following judgment is made. First. The presence of silicon and germanium can be confirmed by secondary ion mass spectrometry; The size of the unit cell obtained from the (220) diffraction peak angle in the X-ray diffraction method is larger than the crystal cell unit lattice size of 5.43 mm and smaller than the crystal germanium unit cell size of 5.67 mm; 3. 3. In the Raman scattering spectrum, a peak attributed to the silicon-silicon bond of crystalline silicon is observed. The Raman shift value of the peak is shifted to a lower wave number side than the Raman shift value of crystalline silicon not containing germanium; When a peak near 400 cm ⁻¹ attributed to crystalline silicon germanium is observed, and when the first, second and third conditions are satisfied simultaneously among these five conditions, the first, third and fourth conditions are satisfied. When satisfying at the same time, or when satisfying the first, third and fifth conditions at the same time, it is considered that the crystalline silicon germanium phase is present, that is, it is determined to be microcrystalline silicon germanium.

  When the germanium concentration is relatively low, it is difficult to observe a peak attributed to crystalline silicon germanium related to the fifth condition. Therefore, the above first to fourth conditions are mainly used as conditions for determining the presence or absence of crystalline silicon germanium.

  Moreover, a super straight type is mentioned as a structure of a general thin film silicon solar cell. In the super straight type structure, a transparent conductive layer, a photoelectric conversion layer, and an electrode layer are laminated in this order on a light transmissive substrate, and are arranged so that light enters from the light transmissive substrate side.

  The photoelectric conversion layer includes a p-type semiconductor layer (hereinafter referred to as a p-type semiconductor layer), an intrinsic semiconductor layer (hereinafter referred to as an i-type semiconductor layer), and an n-type semiconductor layer (hereinafter referred to as an n-type semiconductor layer). In many cases, a pin junction composed of a semiconductor layer is provided. In the following first and second embodiments, a photoelectric conversion device having a super straight pin structure will be described as an example.

  Hereinafter, the photoelectric conversion device and the manufacturing method thereof according to Embodiment 1 of the present invention will be described. In the following description of the embodiments, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.

(Embodiment 1)
FIG. 1 is a cross-sectional view illustrating a configuration of a photoelectric conversion apparatus according to Embodiment 1 of the present invention. As shown in FIG. 1, in the photoelectric conversion device 100 according to Embodiment 1 of the present invention, a photoelectric conversion layer 10 and a reflective layer 17 are laminated on a base material 11 in this order.

<Base material>
The base material 11 includes a translucent substrate 11a and a first conductive layer 11b formed on the translucent substrate 11a. As the translucent substrate 11a, a glass plate, a translucent resin plate having heat resistance such as polyimide or polyvinyl, and a laminate thereof are preferably used.

  However, the material of the translucent substrate 11a is not particularly limited as long as it has high light transmissivity and can structurally support the entire photoelectric conversion device 100. Further, the surface of the translucent substrate 11a may be covered with a metal film, a translucent conductive film, an insulating film, or the like.

  The first conductive layer 11b is made of a transparent conductive material. As the first conductive layer 11b, for example, a single layer or a plurality of layers of transparent conductive films such as ITO (Indium Tin Oxide), tin oxide, and zinc oxide can be used. Since the first conductive layer 11b functions as an electrode, it is preferable to have high electrical conductivity. For this reason, the first conductive layer 11b may be one whose electrical conductivity is improved by adding a small amount of impurities.

  As a method for forming the first conductive layer 11b, known methods such as a sputtering method, a CVD (Chemical Vapor Deposition) method, an electron beam evaporation method, a sol-gel method, a spray method, and an electrodeposition method can be used.

  Moreover, it is preferable that the uneven | corrugated shape is formed in the surface of the 1st conductive layer 11b. This uneven shape can scatter and refract incident light incident from the translucent substrate 11a side, thereby extending the optical path length, increasing the light confinement effect in the photoelectric conversion layer 10 and increasing the short-circuit current density. .

  As a method of forming a concavo-convex shape on the surface of the first conductive layer 11b, after forming the first conductive layer 11b on the translucent substrate 11a, a method of forming the concavo-convex shape by mechanical processing such as etching or sand blasting, A method of using the uneven surface shape formed by crystal growth of the film material when forming the first conductive layer 11b, or a regular uneven surface shape is formed because the crystal growth surface is oriented. You may use the method of using what is done.

  Note that it is more preferable to form a zinc oxide layer on the first conductive layer 11b by sputtering or the like because the first conductive layer 11b can be prevented from being damaged by plasma when the photoelectric conversion layer 10 is formed later.

  In addition, an antireflection layer may be formed between the first conductive layer 11b and the photoelectric conversion layer 10 in order to increase the amount of light incident on the photoelectric conversion layer 10 and increase the short-circuit current density. The refractive index of the antireflection layer is preferably a value between the refractive index of the first conductive layer 11 b and the refractive index of the photoelectric conversion layer 10. Specifically, the refractive index of the antireflection layer is preferably 2.0 or more and 3.0 or less.

  The thickness of the antireflection layer is preferably 30 nm or more and 100 nm or less. The appropriate thickness of the antireflection layer varies depending on the balance with the refractive index of the antireflection layer and the wavelength range of light for which antireflection is desired.

  The antireflection layer may be insulative when formed to be relatively thin, but it is desirable that it has conductivity from the viewpoint of improving the electrical contact between the photoelectric conversion layer 10 and the substrate 11. .

  As the material for the antireflection layer, for example, ITO, tin oxide, zinc oxide, etc., as well as titanium dioxide, niobium oxide, etc., can be used as in the material of the first conductive layer 11b. The antireflection layer may be a single layer or a multilayer film having a single refractive index, or may be a single layer or a plurality of layers having different refractive indexes in the film thickness direction, formed by a method such as a composition gradient method. You may be comprised with the laminated film which consists of.

  As a method for forming the antireflection layer, known methods such as a sputtering method, a CVD method, an electron beam evaporation method, a sol-gel method, a spray method, and an electrodeposition method can be used. Further, similarly to the first conductive layer 11b, it is preferable that an uneven shape is formed on the surface of the antireflection layer.

  As a means for forming the uneven shape on the antireflection layer, the same means as the first conductive layer 11b can be used. However, by forming the antireflection layer on the uneven shape of the first conductive layer 11b, The surface of the prevention layer may have an uneven shape following the uneven shape of the first conductive layer 11b.

  In addition, it is more preferable to form a zinc oxide layer on the antireflection layer by a sputtering method or the like because the antireflection layer can be prevented from being damaged by plasma when the photoelectric conversion layer 10 is formed later.

  In this embodiment, as the base material 11 using the uneven shape formed during the crystal growth of the film material, tin oxide is deposited on a soda glass by a CVD method (trade name: Asahi-, manufactured by Asahi Glass Co., Ltd.). In U), titanium dioxide is deposited by sputtering and zinc oxide is deposited by sputtering.

<Photoelectric conversion layer>
In the photoelectric conversion layer 10 of this embodiment, the p-type semiconductor layer 12, the i-type semiconductor layer 13, and the n-type semiconductor layer 14 are laminated | stacked in an order from the base material 11 side, and the pin junction is comprised.

  The thickness of each semiconductor layer is not particularly limited, but the thickness of the p-type semiconductor layer 12 is 5 nm to 50 nm, the thickness of the i-type semiconductor layer 13 is 100 nm to 5000 nm, and the n-type semiconductor layer 14 The film thickness is preferably 5 nm or more and 100 nm or less. More preferably, the p-type semiconductor layer 12 has a thickness of 10 nm to 30 nm, the i-type semiconductor layer 13 has a thickness of 200 nm to 4000 nm, and the n-type semiconductor layer 14 has a thickness of 10 nm to 30 nm.

  The main material of the constituent material of the photoelectric conversion layer 10 is silicon, and amorphous silicon or microcrystalline silicon is particularly preferable. Here, “amorphous silicon” and “microcrystalline silicon” include “hydrogenated amorphous silicon” and “hydrogenated microcrystalline silicon”, which are generally used in the art.

  The p-type semiconductor layer 12 is a silicon layer doped with a p-type conductivity determining element. As the p-type conductivity determining element, impurity atoms such as boron, aluminum and gallium can be used. The main material of the p-type semiconductor layer 12 may be amorphous silicon or microcrystalline silicon.

  It is preferable that the p-type semiconductor layer 12 contains a crystalline silicon phase because high conductivity can be obtained, the series resistance of the photoelectric conversion layer 10 can be reduced, and the conversion factor of the photoelectric conversion device 100 can be increased to obtain high conversion efficiency. .

  In addition, the p-type semiconductor layer 12 including a crystalline silicon phase is excellent as a base layer for crystallization of the i-type semiconductor layer 13. Specifically, the p-type semiconductor layer 12 containing a crystalline silicon phase makes it easy to grow a crystal component at the initial stage of the formation of the i-type semiconductor layer 13, and the high-quality i-type semiconductor layer 13 having a high crystallization rate. Enables film formation. Therefore, the p-type semiconductor layer 12 including the crystalline silicon phase increases the short-circuit current density of the photoelectric conversion device 100 and contributes to the improvement of conversion efficiency.

  Furthermore, the p-type semiconductor layer 12 preferably contains carbon atoms or nitrogen atoms as impurities. When the p-type semiconductor layer 12 contains the impurities, the open-circuit voltage of the photoelectric conversion device 100 is increased and the conversion efficiency is improved as compared with a photoelectric conversion device having a p-type semiconductor layer not containing the impurities. it can.

  The reason for this is not clear, but (1) the band gap of the p-type semiconductor layer 12 widens and the diffusion potential increases, (2) the interface passivation at the grain boundaries due to the addition of impurities, and the p-type and i-type semiconductor layers. It is conceivable that recombination at the interface is reduced due to the effect of interface passivation with the layer.

  However, a lower impurity concentration is preferable. When the impurity concentration is low, the occurrence of discontinuity or mismatch of the band gap between the p-type semiconductor layer 12 and the i-type semiconductor layer 13 is reduced, so there is no need to provide an interface layer or the like between both layers. A photoelectric conversion device with high conversion efficiency can be obtained easily and inexpensively. For this reason, in this embodiment, the p-type semiconductor layer 12 consists of a microcrystalline silicon layer containing a trace amount of carbon. Note that the p-type semiconductor layer 12 may contain impurities of both carbon atoms and nitrogen atoms.

  The i-type semiconductor layer 13 is a microcrystalline silicon layer to which no impurity is added. However, the i-type semiconductor layer 13 may contain a small amount of an impurity element as long as it is a substantially intrinsic semiconductor. In this case, amorphous silicon may be used as the material of the i-type semiconductor layer 13 instead of microcrystalline silicon.

  However, microcrystalline silicon is preferable to amorphous silicon as a material for the i-type semiconductor layer 13 in that high photoelectric conversion efficiency can be obtained because it does not cause photodegradation. Further, as will be described later, in a photoelectric conversion device having an n-type semiconductor layer 14 made of microcrystalline silicon, i is reduced in order to reduce recombination at the interface between the n-type semiconductor layer 14 and the i-type semiconductor layer 13. The type semiconductor layer 13 is preferably microcrystalline silicon.

  In order to increase the sensitivity of the i-type semiconductor layer 13 to long wavelengths, the i-type semiconductor layer 13 may contain at least one of amorphous silicon germanium and microcrystalline silicon germanium. In this case, the atomic composition percentage of germanium in the i-type semiconductor layer 13 is preferably 5 atomic% or more and 30 atomic% or less.

  If the atomic composition percentage of germanium is less than 5 atomic%, the band gap is hardly reduced, and thus the short circuit current density of the photoelectric conversion device cannot be increased, which is not preferable. When the atomic composition percentage of germanium exceeds 30 atomic%, the band gap decreases and the open circuit voltage of the photoelectric conversion device decreases, or the crystal grain size of the i-type semiconductor layer 13 decreases and the conversion efficiency of the photoelectric conversion device is reduced. Is unfavorable because of lowering.

  The n-type semiconductor layer 14 is a silicon layer doped with an n-type conductivity determining element. As the n-type conductivity determining element, impurity atoms such as phosphorus, nitrogen and oxygen can be used. The main material of the n-type semiconductor layer 14 may be amorphous silicon or microcrystalline silicon. It is preferable that the n-type semiconductor layer 14 includes crystalline silicon because high conductivity can be obtained, the series resistance of the photoelectric conversion layer 10 can be reduced, and the conversion factor of the photoelectric conversion device 100 can be increased to obtain high conversion efficiency.

  The n-type semiconductor layer 14 preferably contains carbon atoms or nitrogen atoms as impurities. When the n-type semiconductor layer 14 contains the impurities, the open-circuit voltage of the photoelectric conversion device 100 is increased and the conversion efficiency is improved as compared with a photoelectric conversion device having an n-type semiconductor layer not containing the impurities. it can.

  The reason for this is not clear, but (1) the band gap of the n-type semiconductor layer 14 widens and the diffusion potential increases, (2) the interface passivation at the grain boundaries due to the addition of impurities, and the i-type and n-type semiconductor layers. It is conceivable that recombination at the interface is reduced due to the effect of interface passivation with the layer. In the present embodiment, the n-type semiconductor layer 14 is made of microcrystalline silicon. Note that the n-type semiconductor layer 14 may contain impurities of both carbon atoms and nitrogen atoms.

  When at least one of the p-type semiconductor layer 12 and the n-type semiconductor layer 14 contains a carbon atom as an impurity, the silicon carbide crystal phase is not substantially contained. This state can be confirmed by, for example, that when a Raman scattering spectrum of microcrystalline silicon containing a carbon atom is observed, a peak attributed to a silicon-carbon bond constituting the silicon carbide crystal is not substantially detected. it can. This state can also be confirmed by substantially not detecting a diffraction peak attributed to the silicon carbide crystal structure in the X-ray diffraction method.

  As a method for forming the photoelectric conversion layer 10, a CVD method can be used. Examples of the CVD method include atmospheric pressure CVD, reduced pressure CVD, plasma CVD, thermal CVD, hot wire CVD, and MOCVD (Metal Organic Chemical Vapor Deposition) method. In this embodiment, the plasma CVD method is used.

The silicon-containing gas used when forming the photoelectric conversion layer 10 by the plasma CVD method is not particularly limited as long as it contains silicon atoms such as SiH ₄ and Si ₂ H _6, but generally SiH ₄ is used. .

As a dilution gas used together with the silicon-containing gas, H ₂ gas, Ar gas, and He gas can be used, but H ₂ gas is generally used when forming amorphous silicon and microcrystalline silicon.

Further, when forming the p-type semiconductor layer 12 and the n-type semiconductor layer 14, a doping gas is used together with the silicon-containing gas and the dilution gas. The doping gas is not particularly limited as long as it contains a target type conductivity determining element. Generally, when the p-type conductivity determining element is boron, B ₂ H ₆ is used as the n-type conductivity. PH ₃ is used when the sex determining element is phosphorus.

  When the photoelectric conversion layer 10 is formed by the plasma CVD method, the abundance ratio between the amorphous phase and the crystalline phase is controlled by appropriately controlling the film forming parameters such as the substrate temperature, pressure, gas flow rate, and power input to the plasma. It is possible to control.

<Reflective layer>
In the reflective layer 17 of this embodiment, the 2nd conductive layer 15, the low-refractive-index layer 16b, and the back surface electrode 16 are laminated | stacked in order from the base material 11 side. Specifically, a low refractive index layer 16 b having a lower refractive index and translucency than the second conductive layer 15 is located on the second conductive layer 15. The back electrode 16 that is in contact with and electrically connected to a part of the second conductive layer 15 is located on the low refractive index layer 16b.

<Back electrode>
The back surface electrode 16 should just be comprised by the at least 1 or more layers of conductive layer, and the light reflectivity and electrical conductivity of a conductive layer are so preferable that it is high. As a material for the back electrode 16, a metal material such as silver, aluminum, titanium and palladium, or an alloy thereof, which has high visible light reflectivity, can be used. The back electrode 16 is formed on the photoelectric conversion layer 10 by a CVD method, a sputtering method, a vacuum evaporation method, an electron beam evaporation method, a spray method, a screen printing method, or the like.

  The back electrode 16 reflects the light that has not been absorbed in the photoelectric conversion layer 10 and returns it to the photoelectric conversion layer 10, which contributes to improving the conversion efficiency of the photoelectric conversion device 100. The thickness of the back electrode 16 is preferably 100 nm or more and 400 nm or less.

<Second conductive layer>
By forming the second conductive layer 15 between the photoelectric conversion layer 10 and the back electrode 16, it is possible to improve the light confinement effect and the light reflectance with respect to incident light. Furthermore, by forming the second conductive layer 15, it is possible to prevent the elements contained in the back electrode 16 from diffusing into the photoelectric conversion layer 10.

  The second conductive layer 15 is formed by the same material and manufacturing method as the first conductive layer 11b. In addition, the thickness of the 2nd conductive layer 15 should just be 20 nm or more. However, if the second conductive layer 15 is too thick, the amount of light that reenters the photoelectric conversion layer 10 decreases due to light absorption that occurs in the second conductive layer 15. Therefore, the thickness of the second conductive layer 15 is preferably 20 nm or more and 3000 nm or less.

<Low refractive index layer>
JOURNAL OF APPLIED PHYSICS Vol.95, No.3, 1 February 2004 pp1427-1429 (Non-Patent Document 2) is a prior art document that considers the relationship between the refractive index of a dielectric in contact with the back electrode 16 and surface plasmon absorption. .

  Non-Patent Document 2 IV. It is described in DISCUSION that the surface plasmon absorption shifts to the longer wavelength side as the refractive index of the dielectric in contact with Ag having a rough surface is higher.

  A feature of the present invention is that when the low refractive index layer 16b is not provided by providing the low refractive index layer 16b having a refractive index lower than that of the second conductive layer 15 between the second conductive layer 15 and the back electrode 16. In comparison, the surface plasmon absorption generated at the interface between the back electrode 16 and the low refractive index layer 16b is shifted to the low wavelength side.

  In a normal super straight type thin film silicon photoelectric conversion device, the light reaching the back electrode 16 hardly contains light having a short wavelength shorter than 700 nm. That is, in the ratio of the light reaching the back electrode 16, the long wavelength light is more than the short wavelength light.

  For this reason, the low refractive index layer 16b is provided to suppress the light absorption phenomenon with respect to light having a long wavelength, thereby increasing the amount of light reflected by the back electrode 16 and re-entering the photoelectric conversion layer 10, and the photoelectric conversion device 100. The conversion efficiency can be increased.

  The low refractive index layer 16b may be formed using the same material and manufacturing method as the first conductive layer 11b and the second conductive layer 15, or may be formed using other materials. When the low refractive index layer 16b is formed using the same material as the first conductive layer 11b and the second conductive layer 15, in order to make the refractive index of the low refractive index layer 16b lower than that of the second conductive layer 15, for example, The carrier concentration of the low refractive index layer 16 b needs to be higher than the carrier concentration of the second conductive layer 15.

  However, in the low refractive index layer 16b, when the carrier concentration becomes high, the extinction coefficient increases and the light absorption rate in the low refractive index layer 16b increases. Therefore, it is necessary to form the low refractive index layer 16b in consideration of the balance between these relationships and the film thickness.

Specifically, when the low refractive index layer 16b is formed by doping zinc oxide with gallium, the refractive index for light with a wavelength of 1000 nm is 1.9 when the carrier concentration is about 3 × 10 ¹⁹ atoms / cm ^3. The extinction coefficient is 9 × 10 ⁻⁴ . When the carrier concentration is about 7 × 10 ²⁰ atoms / cm ³ , the refractive index is 1.4 and the extinction coefficient is 6 × 10 ⁻² .

  Thus, as the carrier concentration increases, the light absorption rate of the low refractive index layer 16b having the same film thickness increases. For example, when the film thickness of the low refractive index layer 16b is 80 nm, increasing the carrier concentration as described above increases the light absorption rate of the low refractive index layer 16b by about 5%.

As materials of the low refractive index layer 16b, materials other than those mentioned in the first conductive layer 11b and the second conductive layer 15 include inorganic oxides such as SiO ₂ , Al ₂ O ₃ or MgO, CaCO ₃ , K _2. Inorganic carbonates such as CO ₃ , BaCO ₃ or SrCO ₃ , inorganic halides such as KBr, NaBr, NaF, CaF ₂ , LiF, MgF ₂ , BaF ₂ or SrF ₂ , inorganic sulfates such as BaSO ₄ Can be used alone or in combination.

  Alternatively, the low refractive index layer 16b may be formed using a material whose electrical conductivity is improved by doping impurities into these materials or utilizing oxygen vacancies.

Of the above materials, SiO ₂ , Al ₂ O _3, or MgF ₂ is a stable material and easy to handle, and generally has a low light absorption rate and a refractive index of about 1.4. Since the refractive index is lower than the material of the second conductive layer 15, it is preferable as the material of the low refractive index layer 16b. Among these, SiO ₂ is particularly preferable because it is an inert substance that has a high chemical stability in itself and hardly affects the second conductive layer 15 and the back electrode 16 that are in contact with each other.

The film thickness of the low refractive index layer 16b is preferably 30 nm or more and 100 nm or less. In this embodiment, the low refractive index layer 16b is formed by sputtering using SiO ₂ having a refractive index of 1.45 with respect to light having a wavelength of 1000 nm so as to have a film thickness of 50 nm. .

<Shape of contact portion between second conductive layer and back electrode>
The back electrode 16 is in contact with a part of the second conductive layer 15. Thereby, even when the low refractive index layer 16b is formed of a material having electrical insulation, it is possible to extract current from the photoelectric conversion layer 10 without passing through the low refractive index layer 16b.

  In order to form the above structure, the low refractive index layer 16 b may be formed so as not to cover the entire surface of the second conductive layer 15. For example, the low refractive index layer 16b can be formed using a known method such as a metal mask or photolithography. By using these methods, a portion of the second conductive layer 15 is masked to form a material for the low refractive index layer 16b, so that the material for the low refractive index layer 16b is formed on the masked portion of the second conductive layer 15. No film is formed. Thereafter, by removing the mask and forming the back electrode 16, a structure in which a part of the second conductive layer 15 and the back electrode 16 are in contact with each other can be formed.

  In addition, since the light absorption phenomenon can be suppressed as the area where the back electrode 16 and the low refractive index layer 16 b are in contact with each other, the short-circuit current density of the photoelectric conversion device 100 can be increased. However, since the area where the second conductive layer 15 and the back electrode 16 are in contact with each other is reduced, the current extraction efficiency is deteriorated and the curve factor is reduced.

  Therefore, the contact area between the second conductive layer 15 and the back electrode 16 has a suitable range for obtaining high photoelectric conversion efficiency. As will be described later, the range is 5.5% to 55% of the entire area of the back electrode.

  Further, by devising the shape of the contact portion between the second conductive layer 15 and the back electrode 16, the current extraction efficiency can be further improved. FIG. 2 is a plan view of the shape of the contact portion between the second conductive layer and the back electrode according to the present embodiment as viewed from the direction of arrow II in FIG. In FIG. 2, the back surface electrode 16 is illustrated transparently.

  In the present embodiment, as shown in FIG. 2, the shape of the contact portion between the second conductive layer 15 and the back electrode 16 is a grid shape in plan view. Specifically, a subgrid 16c that extends in parallel with a distance from each other, and a main grid 16a that extends in a direction orthogonal to the extending direction of the subgrid 16c and is connected to all the subgrids 16c. Is formed.

  By configuring the contact portion between the second conductive layer 15 and the back electrode 16 with the main grid 16a and the subgrid 16c, current can be collected from the entire surface of the photoelectric conversion layer 10, and current extraction efficiency is improved. Become.

  The line width of the subgrid 16c is preferably 0.01 mm or more and 1 mm or less in consideration of the mask processing accuracy and the like. Moreover, since the main grid 16a has a function of collecting the current collected from the sub-grid 16c, the main grid 16a is preferably thicker than the sub-grid 16c, and preferably 0.1 mm or more and 5 mm or less.

  Note that the number and the pitch of the subgrids 16 c are appropriately designed depending on the conductivity of the second conductive layer 15. When the conductivity of the second conductive layer 15 is relatively high, the electrical resistance does not become so high even when the current passes through the second conductive layer 15, so that the interval between the sub-grids 16 c can be widened. On the other hand, when the conductivity of the second conductive layer 15 is low, it is necessary to narrow the interval between the subgrids 16c. Therefore, it is preferable that the interval between the subgrids 16c be 0.5 mm or more and 2 mm or less in consideration of the conductivity of the second conductive layer 15. In addition, the position of the main grid 15a is not necessarily provided in the in-plane center portion of the photoelectric conversion device 100, and may be provided in the end portion.

  In the present embodiment, the line width of the sub-grid 16c is 0.1 mm to 1 mm, and the line width of the main grid 16a is 0.2 mm to 5 mm. The interval between the subgrids 16c is set to 0.75 mm or more and 1.875 mm or less.

  Further, the distance from the end of the photoelectric conversion device 100 to the subgrid 16c located closest to the end is 1 mm, and the distance from the end of the photoelectric conversion device 100 to the main grid 16a is 1 mm.

The area of the photoelectric conversion device 100 is 100 mm ² , and the contact area between the second conductive layer 15 and the back electrode 16 is 5.5% to 55% of the total area of the back electrode 16.

  With the above configuration, a super straight photoelectric conversion device 100 with high short-circuit current density and high conversion efficiency can be manufactured.

  Hereinafter, a photoelectric conversion device and a manufacturing method thereof according to Embodiment 2 of the present invention will be described. Since the photoelectric conversion device according to this embodiment is different from the photoelectric conversion device 100 according to Embodiment 1 only in that it is a tandem type, the description of other components will not be repeated.

(Embodiment 2)
FIG. 3 is a cross-sectional view illustrating a configuration of a photoelectric conversion apparatus according to Embodiment 2 of the present invention. As shown in FIG. 3, the tandem photoelectric conversion apparatus 200 according to Embodiment 2 of the present invention includes first and second photoelectric conversion layers 10 and 20. In the second photoelectric conversion layer 20, a p-type semiconductor layer 22, an i-type semiconductor layer 23, and an n-type semiconductor layer 24 are stacked in order from the base material 11 side to form a pin junction.

  In a tandem thin film silicon solar cell, the pin junction closest to the light incident side is often referred to as a top cell, and the pin junction farthest from the light incident side is referred to as a bottom cell. In a tandem photoelectric conversion device having three or more pin junctions, the pin junction located between the top cell and the bottom cell is often referred to as a middle cell.

  The tandem photoelectric conversion device 200 according to the present embodiment is a photoelectric conversion device having a super straight type structure. In the tandem photoelectric conversion device 200, the first photoelectric conversion layer 10, the second photoelectric conversion layer 20, and the reflection layer 17 are laminated on the base material 11 in this order.

  Since the first photoelectric conversion layer 10 is located on the light incident side, only the light transmitted through the first photoelectric conversion layer 10 is incident on the second photoelectric conversion layer 20. Therefore, in the tandem photoelectric conversion device 200, the first and second photoelectric conversion layers 10 and 20 can receive different spectral regions of incident light, so that the light use efficiency can be improved. A high open-circuit voltage substantially equal to the sum of the open-circuit voltages of the two photoelectric conversion layers 10 and 20 can be obtained.

  Further, by making the band gap of the first photoelectric conversion layer 10 located on the light incident side larger than the band gap of the second photoelectric conversion layer 20, short wavelength light of the incident light is mainly used for the first photoelectric conversion layer. In the conversion layer 10, long-wavelength light is mainly absorbed by the second photoelectric conversion layer 20, so that the conversion efficiency of the tandem photoelectric conversion device 200 can be further improved.

  Examples of silicon-based materials having different band gaps include amorphous silicon carbide, amorphous silicon, amorphous silicon germanium, amorphous germanium, microcrystalline silicon, microcrystalline silicon germanium, and microcrystalline germanium. These can be appropriately selected and used as the light absorption layer.

  For example, in a typical two-junction thin-film silicon solar cell using amorphous silicon for the top cell and microcrystalline silicon for the bottom cell, amorphous silicon having a large band gap absorbs light in the short wavelength region of the incident light. However, microcrystalline silicon having a small band gap is designed to absorb the remaining light in the long wavelength region.

  Microcrystalline silicon and microcrystalline silicon germanium are known not to cause photodegradation as described above, and are generally preferred for use as materials that absorb light of long wavelengths in multi-junction thin-film silicon solar cells. It has been.

  In the first and second photoelectric conversion layers 10 and 20, it is only necessary that the stacking directions of the pin junctions are the same and that the p-type semiconductor layers 12 and 22 are positioned on the light incident side. The same applies when there are three or more photoelectric conversion layers. That is, when the first photoelectric conversion layer 10 has a pin junction, the second photoelectric conversion layer 20 also has a pin junction, and when the first photoelectric conversion layer 10 has a nip junction, the second photoelectric conversion layer. 20 also has a nip junction.

  The thickness of each semiconductor layer in the first and second photoelectric conversion layers 10 and 20 is not particularly limited, but in the first photoelectric conversion layer 10, the thickness of the p-type semiconductor layer 12 is 5 nm or more. It is preferable that the thickness of the i-type semiconductor layer 13 is 50 nm or less, the thickness of the i-type semiconductor layer 13 is 100 nm or more and 500 nm or less, and the thickness of the n-type semiconductor layer 14 is 5 nm or more and 50 nm or less. More preferably, the p-type semiconductor layer 12 has a thickness of 10 nm to 30 nm, the i-type semiconductor layer 13 has a thickness of 200 nm to 400 nm, and the n-type semiconductor layer 14 has a thickness of 10 nm to 30 nm.

  In the second photoelectric conversion layer 20, the p-type semiconductor layer 22 has a thickness of 5 nm to 50 nm, the i-type semiconductor layer 23 has a thickness of 1000 nm to 5000 nm, and the n-type semiconductor layer 24 has a thickness of 5 nm to 100 nm. The following is preferable. More preferably, the p-type semiconductor layer 22 has a thickness of 10 nm to 30 nm, the i-type semiconductor layer 23 has a thickness of 2000 nm to 4000 nm, and the n-type semiconductor layer 24 has a thickness of 10 nm to 30 nm.

  An intermediate layer may be formed between at least one pair of mutually adjacent pin junctions or nip junctions among the plurality of pin junctions or the plurality of nip junctions. That is, an intermediate layer may be formed between the first photoelectric conversion layer 10 and the second photoelectric conversion layer 20. When there are three or more photoelectric conversion layers, an intermediate layer may be formed in at least one place between the photoelectric conversion layers. The intermediate layer is preferably composed of a light-transmitting conductive film.

  By providing the intermediate layer, a part of the light that has passed through the first photoelectric conversion layer 10 and is incident on the intermediate layer is reflected by the intermediate layer, and the rest is transmitted through the intermediate layer to the second photoelectric conversion layer 20. Since the light enters, the amount of light incident on each photoelectric conversion layer can be controlled.

  Thereby, the value of the photocurrent in the 1st and 2nd photoelectric converting layers 10 and 20 can be equalized. By efficiently using the photogenerated carriers generated in the first and second photoelectric conversion layers 10 and 20, the conversion efficiency can be improved by increasing the short-circuit current value of the tandem photoelectric conversion device 200.

  In the tandem photoelectric conversion device 200, the low refractive index layer 16 b is provided between the second conductive layer 15 and the back electrode 16 by providing the low refractive index layer 16 b having a refractive index lower than that of the second conductive layer 15. Compared to the case where there is no surface plasmon absorption, the surface plasmon absorption generated at the interface between the back electrode 16 and the low refractive index layer 16b is shifted to the low wavelength side.

  By providing the low refractive index layer 16b and suppressing the light absorption phenomenon with respect to light having a long wavelength, the amount of light reflected by the back electrode 16 and re-entering the first and second photoelectric conversion layers 10 and 20 is increased. Thus, the conversion efficiency of the tandem photoelectric conversion device 200 can be increased.

  With the above configuration, a super straight tandem photoelectric conversion device 200 with high short-circuit current density and high conversion efficiency can be manufactured.

  The present invention can also be applied to a substrate type photoelectric conversion device. Embodiment 3 in which the present invention is applied to a substrate-type photoelectric conversion device will be described with reference to the drawings. Since the photoelectric conversion apparatus 300 according to the present embodiment is different from the photoelectric conversion apparatus 100 according to the first embodiment only in that it is a substrate type, the description of other configurations will not be repeated.

(Embodiment 3)
FIG. 4 is a cross-sectional view illustrating a configuration of a photoelectric conversion apparatus according to Embodiment 3 of the present invention. As shown in FIG. 4, in the substrate type photoelectric conversion apparatus 300 according to Embodiment 3 of the present invention, the reflective layer 17, the photoelectric conversion layer 10, and the first conductive layer 11b are provided on the support substrate 11c. They are formed in this order.

  The structure shown in FIG. 4 can be formed by forming the low refractive index layer 16b so as not to cover the back electrode 16 uniformly. As a method for forming the low refractive index layer 16b so as not to cover the back electrode 16 uniformly, there is a method using a metal mask or the like as described above.

  In the present embodiment, since light enters from the first conductive layer 11b side, the support substrate 11c may be made of a non-light-transmitting material. Or like the translucent board | substrate 11a, the support substrate 11c may be comprised with the material which has translucency. As a material of the support substrate 11c, the same material as the translucent substrate 11a can be used. In addition, the support substrate 11c may be made of a metal plate such as a stainless plate or a copper plate. The thickness of the support substrate 11c is not particularly limited as long as it is strong enough to structurally support the entire photoelectric conversion device 300.

  In the present embodiment, unevenness (not shown) for improving the light confinement effect is formed on the support substrate 11c. However, the support substrate 11c may be formed by forming a transparent conductive film having unevenness on the support substrate 11c or processing the unevenness on the back electrode 16 without having the unevenness. As a result, it is desirable that irregularities having a surface roughness RMS (root mean square roughness) of 20 nm or more and 200 nm or less are formed on the back electrode 16.

  Due to the unevenness, the light confinement effect in the reflective layer 17 itself is exhibited, and unevenness due to the uneven shape on the back electrode 16 is formed on the surface after the first conductive layer 11b is deposited. Can also obtain the light confinement effect.

  According to the present embodiment, the surface plasmon absorption generated at the interface between the back electrode 16 and the low refractive index layer 16b can be reduced, so that the photoelectric conversion efficiency of the substrate type photoelectric conversion device 300 can be improved.

  In addition, the substrate type photoelectric conversion device 300 according to the present embodiment has a pin structure from the light incident side, similarly to the structure of the super straight type photoelectric conversion device 100 according to the first embodiment. It may have a nip structure from the light incident side.

  In addition, a collecting electrode may be formed on the first conductive layer 11b. As the material for the current collecting electrode, a material having high conductivity such as silver is preferably used like the back electrode 16. In the case where the current collecting electrode is formed of a non-translucent material, the current collecting electrode can block light incident on the photoelectric conversion layer 10 and reduce the photoelectric conversion efficiency of the photoelectric conversion device. The area of the electrode is preferably small.

Hereinafter, experimental examples in which the power generation characteristics of the photoelectric conversion device according to the present invention are confirmed will be described.
(Experimental example)
(Examples 1-5)
In Examples 1-5, the super straight type photoelectric conversion apparatus 100 shown in FIG. 1 was produced as follows.

  As the base material 11, a blue plate glass (Asahi Glass Co., Ltd.) having a length of 115 mm × width of 115 mm × thickness of 3.9 mm, in which a first conductive layer 11 b made of a tin oxide-based transparent conductive film is formed on the surface of a translucent substrate 11 a. Manufactured, trade name: Asahi-VU).

  On the base material 11, titanium dioxide was deposited to a thickness of 70 nm by a sputtering method, and zinc oxide was further deposited to a thickness of 10 nm by a sputtering method.

  Thereafter, the p-type semiconductor layer 12, the i-type semiconductor layer 13, and the n-type semiconductor layer 14 were sequentially stacked by plasma CVD under the conditions described later to form the photoelectric conversion layer 10. Subsequently, zinc oxide is sequentially deposited on the photoelectric conversion layer 10 so as to have a thickness of 80 nm as the second conductive layer 15 and silver as the back electrode 16 so as to have a thickness of 400 nm. A type photoelectric conversion device 100 was produced.

Each layer of the photoelectric conversion layer 10 was formed under the following conditions. In forming the p-type semiconductor layer 12, a mixed gas containing SiH ₄ , H ₂ and B ₂ H ₆ was used as a source gas. The gas flow ratio of H _{2 to} SiH ₄ was 150 times, and the gas flow ratio of B ₂ H ₆ to SiH ₄ was 0.003 times.

  The p-type semiconductor layer 12 is desirably thin as long as it does not impair the function as the p-type semiconductor layer in order to increase the amount of light incident on the i-type semiconductor layer 13 that is a photoactive layer. The film thickness was taken.

For the formation of the i-type semiconductor layer 13, a mixed gas containing SiH ₄ and H ₂ was used as a source gas. The gas flow ratio of H _{2 to} SiH ₄ was 80 times. In this example, the film thickness of the i-type semiconductor layer 13 was 2500 nm.

For the formation of the n-type semiconductor layer 14, a mixed gas containing SiH ₄ , H ₂ , PH ₃ and N ₂ was used as a source gas. The gas flow ratio of H _{2 to} SiH ₄ was 100 times, and the gas flow ratio of PH _{3 to} SiH ₄ was 0.03 times.

  The film thickness of the n-type semiconductor layer 14 is preferably as thin as not to impair the function as the n-type semiconductor layer in order to suppress absorption of reflected light from the back electrode 16. In this embodiment, the film thickness is 20 nm. did. The substrate temperature at the time of forming the p-type, i-type and n-type semiconductor layers 12, 13, and 14 by plasma CVD was set to 180 ° C.

Subsequently, zinc oxide was deposited as the second conductive layer 15 to a thickness of 80 nm by a sputtering method. Thereafter, as a low refractive index layer 16b, a metal mask was attached, and SiO ₂ was deposited to a thickness of 50 nm by a sputtering method.

  By appropriately changing the area of the opening of the metal mask, the contact area between the second conductive layer 15 and the back electrode 16 formed in a subsequent process was changed. The contact area between the second conductive layer 15 and the back electrode 16 in plan view is 5.5% in Example 1, 10% in Example 2, and 45% in Example 3 with respect to the entire area of the back electrode 16. In Example 4, it was 45%, and in Example 5, it was 55%. The shape of the contact portion between the second conductive layer 15 and the back electrode 16 was a grid.

  Thereafter, the metal mask was removed, and silver was deposited as the back electrode 16 to a thickness of 120 nm.

For such a photoelectric conversion device of Examples 1 to 5 obtained in the, AM 1.5, under the conditions of irradiance 100 mW / cm ^2, current cell area 1 cm ² - voltage characteristics were measured.

Short-circuit current density, Example 1, 23.6mA / cm ^2, Example 2, 23.5mA / cm ^2, Example 3, 23.3mA / cm ^2, Example 4, 23.3mA / cm ^2, carried In Example 5, it was 23.2 mA / cm ² .

  The open circuit voltage was 0.512 V in Example 1, 0.512 V in Example 2, 0.511 V in Example 3, 0.512 V in Example 4, and 0.512 V in Example 5.

  The fill factor was 0.714 in Example 1, 0.715 in Example 2, 0.715 in Example 3, 0.714 in Example 4, and 0.715 in Example 5.

  The series resistance was 6Ω in Example 1, 6Ω in Example 2, 6Ω in Example 3, 6Ω in Example 4, and 6Ω in Example 5.

  The conversion efficiencies were 8.63% in Example 1, 8.60% in Example 2, 8.51% in Example 3, 8.52% in Example 4, and 8.49% in Example 5. It was.

As a comparative example, a photoelectric conversion device was manufactured under the following conditions.
(Comparative Example 1)
In Comparative Example 1, a super straight type photoelectric conversion device was prepared under the same conditions as in Example 1 except that the low refractive index layer 16b was not formed. Since the low refractive index layer 16b is not formed, a metal mask is not used. Therefore, the second conductive layer 15 and the back electrode 16 are in uniform contact over the entire surface. That is, in Comparative Example 1, the contact area between the second conductive layer 15 and the back electrode 16 in plan view was 100% with respect to the entire area of the back electrode 16.

Photoelectric conversion device of Comparative Example 1, AM 1.5, under the conditions of irradiance 100 mW / cm ^2, current cell area 1 cm ² - voltage characteristics were measured.

In Comparative Example 1, the short-circuit current density was 23.0 mA / cm ² , the open circuit voltage was 0.511 V, the fill factor was 0.715, the series resistance was 6Ω, and the conversion efficiency was 8.40%.

(Comparative Example 2)
In Comparative Example 2, a super straight type photoelectric conversion device was produced under the same conditions as in Example 1 except that a metal mask was not used when forming the low refractive index layer 16b. Since the metal mask is not used, the second conductive layer 15 and the back electrode 16 are not in contact at all. That is, in Comparative Example 2, the contact area between the second conductive layer 15 and the back electrode 16 in plan view was 0% with respect to the entire area of the back electrode 16.

Photoelectric conversion device of Comparative Example 2, AM 1.5, under the conditions of irradiance 100 mW / cm ^2, current cell area 1 cm ² - voltage characteristics were measured.

In Comparative Example 2, the short-circuit current density was 8.2 mA / cm ² , the open circuit voltage was 0.182 V, the fill factor was 0.255, the series resistance was 500Ω, and the conversion efficiency was 0.38%.

(Comparative Example 3)
In Comparative Example 3, a super straight type photoelectric conversion device was formed under the same conditions as in Example 1 except that a metal mask having a uniform opening instead of a grid shape was used when forming the low refractive index layer 16b. Created. In Comparative Example 3, the contact area between the second conductive layer 15 and the back electrode 16 in plan view was 5.5% with respect to the entire area of the back electrode 16.

Photoelectric conversion device of Comparative Example 3, AM 1.5, under the conditions of irradiance 100 mW / cm ^2, current cell area 1 cm ² - voltage characteristics were measured.

In Comparative Example 3, the short-circuit current density was 23.4 mA / cm ² , the open circuit voltage was 0.502 V, the fill factor was 0.533, the series resistance was 22Ω, and the conversion efficiency was 6.26%.

(Comparative Example 4)
In Comparative Example 4, a super straight type photoelectric conversion device was created under the same conditions as in Example 1 except that the sub-grid 16c and the main grid 16a were thinned. In Comparative Example 4, the contact area between the second conductive layer 15 and the back electrode 16 in plan view was 4.5% with respect to the entire area of the back electrode 16.

For the photoelectric conversion device of Comparative Example 4, AM 1.5, under the conditions of irradiance 100 mW / cm ^2, current cell area 1 cm ² - voltage characteristics were measured.

In Comparative Example 4, the short-circuit current density was 23.6 mA / cm ² , the open-circuit voltage was 0.512 V, the fill factor was 0.698, the series resistance was 7Ω, and the conversion efficiency was 8.43%.

(Comparative Example 5)
In Comparative Example 5, a super straight type photoelectric conversion device was created under the same conditions as in Example 1 except that the sub-grid 16c and the main grid 16a were thickened. In Comparative Example 5, the contact area between the second conductive layer 15 and the back electrode 16 in plan view was 63.5% with respect to the entire area of the back electrode 16.

For the photoelectric conversion device of Comparative Example 5, AM 1.5, under the conditions of irradiance 100 mW / cm ^2, current cell area 1 cm ² - voltage characteristics were measured.

In Comparative Example 5, the short-circuit current density was 23.0 mA / cm ² , the open circuit voltage was 0.512 V, the fill factor was 0.716, the series resistance was 6Ω, and the conversion efficiency was 8.43%.

  Hereinafter, the experimental results of Examples 1 to 5 and Comparative Examples 1 to 5 will be considered. Table 1 summarizes the experimental results of Examples 1 to 5 and Comparative Examples 1 to 5.

(Comparison between Examples 1-5 and Comparative Examples 1, 4, 5)
The photoelectric conversion devices of Examples 1 to 5 having a structure in which the low refractive index layer 16b is formed between the second conductive layer 15 and the back electrode 16, and the second conductive layer 15 and the back electrode 16 are partially in contact with each other. Then, compared with the comparative example 1 which did not form the low-refractive-index layer 16b, the high short circuit current density was obtained. This is considered to be because the light absorption phenomenon at the back electrode 16 was suppressed.

  In the photoelectric conversion device of Comparative Example 4 in which the contact area between the second conductive layer 15 and the back electrode 16 is 4.5% with respect to the total area of the back electrode 16, the second conductive layer 15 and the back electrode 16 In comparison with the photoelectric conversion devices of Examples 1 to 5 in which the contact area is 5.5% or more and 55% or less with respect to the entire area of the back electrode 16, the curve factor is reduced due to the increase in series resistance, and the conversion efficiency Decreased. This is considered to be due to the fact that the distance that the photogenerated carriers pass through the second conductive layer 15 is increased due to the increase in the spacing between the grids, and the electrical resistance in the second conductive layer 15 is increased.

  In the photoelectric conversion device of Comparative Example 5 in which the contact area between the second conductive layer 15 and the back electrode 16 is 63.5% with respect to the entire area of the back electrode 16, the current can be sufficiently taken out, so that the fill factor However, the short circuit current density did not increase. This is presumably because the effect of suppressing the light absorption phenomenon was small because the area where the low refractive index layer 16b is formed is too small.

(Comparison between Example 1 and Comparative Example 2)
In the photoelectric conversion device of Comparative Example 2 in which the second conductive layer 15 and the back electrode 16 are not in contact with each other, the photoelectric conversion device of Example 1 in which the second conductive layer 15 and the back electrode 16 are partially in contact. As the series resistance increased, the fill factor decreased. Moreover, the short circuit current density also decreased. This is because, since the low refractive index layer 16b is made of insulating SiO ₂ , when the carriers pass through the low refractive index layer 16b and reach the back electrode 16 in the photoelectric conversion device of Comparative Example 2, the low refractive index layer 16b is low. It is considered that this is because the refractive index layer 16b becomes an electric resistance, which causes a decrease in fill factor and poor current extraction.

(Comparison between Example 1 and Comparative Example 3)
In the photoelectric conversion device of Comparative Example 3 in which the second conductive layer 15 and the back electrode 16 are in contact with each other, but the shape of the contact portion is not a grid shape, the short-circuit current density is the photoelectric conversion device of Example 1. However, the fill factor decreased due to the increase in series resistance, and the conversion efficiency was lower than that of the photoelectric conversion device of Example 1. This is because the distance through which the photogenerated carriers pass through the second conductive layer 15 is increased due to the failure to collect carriers through the entire surface of the back electrode 16, and the electrical resistance in the second conductive layer 15 is increased. This is thought to be due to the increase.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10 first photoelectric conversion layer, 11 base material, 11a translucent substrate, 11b first conductive layer, 11c support substrate, 12, 22 p-type semiconductor layer, 13 i-type semiconductor layer, 14, 24 n-type semiconductor layer, 15 Second conductive layer, 15a, 16a Main grid, 16 Back electrode, 16b Low refractive index layer, 16c Subgrid, 16d Shoulder, 17 Reflective layer, 20 Second photoelectric conversion layer, 100 Super straight type photoelectric conversion device , 200 Super straight type tandem photoelectric conversion device, 300 Substrate type photoelectric conversion device.

Claims (9)

A substrate,
A first conductive layer, a photoelectric conversion layer, a second conductive layer, a low refractive index layer, and a back electrode, which are sequentially disposed on the substrate from the light receiving surface side,
The low refractive index layer has a lower refractive index than the second conductive layer and has translucency,
The back electrode is a photoelectric conversion device in contact with and electrically connected to a part of the second conductive layer. The substrate has translucency;
The first conductive layer is located on the substrate;
The photoelectric conversion layer is located on the first conductive layer,
The second conductive layer is located on the photoelectric conversion layer;
The low refractive index layer is located on the second conductive layer;
The photoelectric conversion device according to claim 1, wherein the back electrode is located on the low refractive index layer. The back electrode is located on the substrate;
The low refractive index layer is located on the back electrode;
The second conductive layer is located on the low refractive index layer;
The photoelectric conversion layer is located on the second conductive layer,
The photoelectric conversion device according to claim 1, wherein the first conductive layer is located on the photoelectric conversion layer. The photoelectric conversion device according to claim 1, wherein the low refractive index layer is made of SiO ₂ .   5. The photoelectric conversion according to claim 1, wherein a contact area between the second conductive layer and the back electrode is 5.5% or more and 55% or less of an entire area of the back electrode in a plan view. apparatus.   6. The photoelectric conversion device according to claim 1, wherein a shape of a contact portion between the second conductive layer and the back electrode is a grid shape in a plan view. On the substrate, the step of forming each layer so that the first conductive layer, the photoelectric conversion layer, the second conductive layer, the low refractive index layer and the back electrode are located in order from the light receiving surface side,
In the step of forming the low refractive index layer, the low refractive index layer is formed of a material having a refractive index lower than that of the second conductive layer and having translucency,
In the step of forming the back electrode, the back electrode is formed so as to be in contact with and electrically connected to a part of the second conductive layer. After the step of forming the first conductive layer, forming the photoelectric conversion layer,
After the step of forming the photoelectric conversion layer, the second conductive layer is formed,
After the step of forming the second conductive layer, forming the low refractive index layer,
The method for manufacturing a photoelectric conversion device according to claim 7, wherein the back electrode is formed after the step of forming the low refractive index layer. After the step of forming the back electrode, the low refractive index layer is formed,
After the step of forming the low refractive index layer, forming the second conductive layer,
After the step of forming the second conductive layer, the photoelectric conversion layer is formed,
The method for manufacturing a photoelectric conversion device according to claim 7, wherein the first conductive layer is formed after the step of forming the photoelectric conversion layer.

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